Transcript for Some Skeptics Think Diana Nyad Had Help Swimming From Cuba to Florida

Next tonight 64-year-old diana nyad was celebrated for that swim from cuba to key west. Today skeptics were saying her triumph was too good to be true. Did she have secret help? She says she'll speak to the critics tomorrow but here is abc's dan harris tonight. Reporter: When she staggered ashore last week, diana nyad, age 64, became an intant icon of perseverance. You're never too old to chase your dream. Reporter: Pretty soon questions came again. Fell low swimmers clunked the numbers. For the first 24 hours she was going 1.6 mile per hour. But then, according to her critics, she appears to have rocketed up to speeds of 3 miles an hour, then 4, then briefly 6 which is faster than an olympic speed swimmer. The community is wondering how her team accounts for that incredible speed. Reporter: Did she hold onto the boat or get in in her team says she got lucky that her strong current helped her paddle in one full day ahead of schedule. There is also the question that according to her blog for a period of 7 hours, nyad apparently did not stop to eat or drink. I said in my own experience in marathon swimming I find it hard to go more than an hour without feeding. It's hard to imagine even if my life depended on it. Reporter: She told the "new york times" she never cheated on anything in her life. If she cheated she had a lot of help. She was accompanied by 40 people. In an era when so many sports heros were brought low, everyone is hoping she'll become not another one. Again, she says she'll answer tomorrow.

This transcript has been automatically generated and may not be 100% accurate.

Now Playing: Rare Look Inside War-Torn Aleppo as Refugees Return After Years Away

Now Playing: {{itm.title}}

{"id":20206629,"title":"Some Skeptics Think Diana Nyad Had Help Swimming From Cuba to Florida","duration":"1:47","description":"64-year-old swimmer plans to address her critics and set the record straight tomorrow via Skype.","url":"/WNT/video/skeptics-diana-nyad-swimming-cuba-florida-20206629","section":"WNT","mediaType":"default"}